Carbonized electrode tube



Feb. 7, 1939. K. M. VAN GESSEL ET AL 2,146,098

CARBONI ZED ELECTRODE TUBE Filed Feb. 20, 1937 INVENTOR KAREL MARINUSVAN GESSEL.

ATTORN EY Patented Feb. 7, 1939 CABBONIZED ELECTRODE TUBE Karel MarinusVan Gessel and Frits Prakke, Eindhoven, Netherlands, assignors to N. V.

Philips Gloeilampenfabrieken,

Netherlands Eindhoven,

Application February 20, 1937, Serial No. 126,740 In Germany February10, 1936 3 Claims.

This invention relates to an electron discharge device comprising one ormore electrodes or other parts with surfaces coated with a carbon layer,and to a method of making an electrode for such 5 a tube.

In order to increase the heat radiation of electrodes for electricdischarge tubes, more particularly of anodes, it is known to coat theseelectrodes on the surface with a black layer such as a carbon layer.Furthermore, it has already been proposed to connect auxiliary bodies,such as cooling ribs to the electrodes and to provide these bodies alsowith a black layer on the surface. Al-

though such layers may yield good results, they present difficulties inmany cases, due to the fact that these electrodes and other bodies maylose part of their coating and black color due to flaking off of thecarbon coating and other elfects caused by high temperatures duringoperation, so that the thermal radiation decreases.

Experiments made by the applicants have proved that these difiicultiesmay be caused by the carbon dissolving'in the underlying material,particularly during the degasifying operation, and that the drawbacks ofthe conventional carbonized electrodes can be avoided by this invention.

Discharge tubes made in accordance with the invention comprise one ormore electrodes or other bodies which are at least partly coated on the30 surface with a carbon layer and in which there r is provided betweenthe core body and the carbon layer a material layer having suchproperties that it strongly adheres to the underlying metal and to thecarbon and in which the carbon of the layer does not or only partlydissolve. For this purpose we prefer to use layers of silicates, such assodium silicate, or layers of refractory oxides, such as one or more ofthe alkaline earths, preferably oxide of magnesium, or oxide ofberyllium, oxides of aluminum, or the like. In this way an electrode isobtained which is coated with a firmly adherent carbon layer and whichretains its heat radiating properties during use, since there ispractically no dissolution of the carbon in the underlying metal layer.

Our invention will better be understood in connection with theaccompanying drawing in which Figure 1 shows a rectifier having an anodeconstructed in accordance with our invention, and Figure 2 is aperspective view partly broken away of part of a cold electrode, such asan anode, made in accordance with our invention.

The rectifier shown in Figure 1 comprises the usual evacuated bulbenclosing a thermionic cathode l such as a tungsten or oxide coatedfilament,

surrounded by an anode 2, preferably of nickel and carbonized inaccordance with our invention. The anode is coated with a firmlyadherent coating of carbon deposited on an intermediate or linking layerof some refractory material which firmly adheres to the metal of theanode and in which the carbon does not dissolve to any substantialextent during operation of the device.

As more clearly shown in Figure 2, the metal body or sheet nickel anodehas on its surface a firmly adherent layer of refractory material,preferably an alkaline earth, such as magnesium oxide. On this layer isan adherent coating of carbon t which may be applied in accordance withwell known methods, but which is preferably deposited by heating theoxide coated electrode in a carbonaceous atmosphere. The linking orbinding layer of oxide seems to link or bind the carbon to the metal andto hinder dissolution of the carbon in the metal.

We have obtained good results with electrodes made in accordance withthe present invention by a method which comprises coating the nickelelec" trode 2 with a layer consisting of one or more alkaline earths,preferably magnesium oxide, by applying to the electrode a materialwhich will produce on.the electrode a thin, dense, adherent layer ofalkaline earth or other oxide when the electrode is treated. Onedesirable way of obtaining this layer is to spray the electrode with asuspension consisting of finely powdered magnesium oxide suspended in avolatile suspending medium, such as water or alcohol, and then bake theelectrode to drive off the suspension medium and leave a firmly adherentlayer of magnesium oxide on the surface of the electrode. Magnesiumcompounds which break down and leave magnesium oxide when heated may beused if desired. The thickness of this layer of refractory oxide is notcritical, but the layer is preferably in view of the low resistance madeas thin as feasible consistent with complete covering of the electrodesurface with a dense, uniform layer of the oxide. The oxide coatednickel electrode is then carbonized by heating it, preferably by theconventional high frequency induction heating coils, in a carbonaceousatmosphere containing a simple hydrocarbon, such as acetylene, methaneor the like. In general, the oxide coated nickel electrode responds tocarbonizing treatment in much the same way as the oxidized or cleannickel electrodes commonly used, and consequently it may be carbonizedby conventional methods, such as, for example, the method disclosed inU. S. patent to Upp, 1,852,865, April 5, 1932.

lib

A cold nickel electrode carbonized in accordance with our inventionwithstands the temperatures attained during operation of theconventional electron discharge devices better than carbonized nickelelectrodes which lack the oxide linking layer and in particular thecarbon coating seems to be more adherent and to remain in place muchbetter, particularly during operation than in the conventionalcarbonized electrodes.

We claim:

1. An electron discharge tube comprising a thermionic cathode and acooperating cold electrode comprising a metal sheet, a thin refractoryadherent layer of magnesium oxide covering the surface of said sheetwhich faces said cathode and a coating of carbon on and firmly adherentto said refractory layer auaoos 2. An electron discharge tube comprisinga thermionic cathode and a cooperating cold electrode comprising a metalsheet, a'linking layer consistingpof one'or more oxides selected fromthe group consisting of the alkaline earths, beryl- I lium oxide, andaluminum oxide and firmly ad-' herent to said metal sheet, and a coatingof carbon on said linking layer. 7

3. An electrode for an electron discharge device comprising a sheet ofnickel having a refractory layer of oxide selected from the groupcomprising the alkaline earths, beryllium oxide and aluminum oxide andfirmly adherent to said nickel sheet, and a coating of carbon on saidlayer.

-KARELMARINUSVANGESSEL. FRITS v

